Specific heat of MgB<sub>2</sub>in a one- and a two-band model from first-principles calculations

Golubov, Alexandre Avraamovitch; Kortus, Jens; Dolgov, O. V.; Jepsen, O.; Kong, Yong; Andersen, O. K.; Gibson, B. J.; Ahn, Kwangwon; Kremer, Reinhard K.

doi:10.1088/0953-8984/14/6/320

Cited by 301 publications

(404 citation statements)

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“…It is of considerable interest to compare these renormalized BCS results with those from full Eliashberg calculations based on the α 2 ij F (ω) spectra given in Ref. [21]. Very similar values of the parameters can also be found in Ref.…”

Section: Rbcs At T=0 For Mgb2supporting

confidence: 55%

Theory of the critical current in two-band superconductors with application toMgB2

Nicol

Ćarbotte

2005

Phys. Rev. B

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Using a Green's function formulation of the superfluid current js, where a momentum qs is applied to the Cooper pair, we have calculated js as a function of qs, temperature, and impurity scattering for a two-band superconductor. We consider both renormalized BCS and full strongcoupling Eliashberg theory. There are two peaks in the current as a function of qs due to the two energy scales for the gaps and this can give rise to non-standard behavior for the critical current. The critical current jc, which is given as the maximum in js, can exhibit a kink as a function of temperature as the maximum is transferred from one peak to other. Other temperature variations are also possible and the universal BCS behavior is violated. The details depend on the material parameters of the system, such as the amount of coupling between the bands, the gap anisotropy, the Fermi velocities, and the density of states of each band. The Ginzburg-Landau relation between jc, the penetration depth λL and thermodynamic critical field Hc, is modified. Using Eliashberg theory with the electron-phonon spectral densities given from bandstructure calculations, we have applied our calculations for js and jc to the case of MgB2 and find agreement with experiment.

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Section: Rbcs At T=0 For Mgb2supporting

confidence: 55%

Theory of the critical current in two-band superconductors with application toMgB2

Nicol

Ćarbotte

2005

Phys. Rev. B

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“…The London equation for a two-gap superconductor is given by 34 we obtain λ L (0) ≈170 nm, consistent with the measured value of λ ab (0) =200±30 nm. The calculated λ L (T ) is shown as the blue curve in Fig.…”

Section: λ and Hc From The Two-band Modelsupporting

confidence: 88%

Measurement of the magnetic penetration depth of a superconducting MgB2thin film with a large intraband diffusivity

et al. 2012

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We report the temperature dependent magnetic penetration depth λ(T ) and the superconducting critical field Hc2(T ) in a 500-nm MgB2 film. Our analysis of the experimental results takes into account the two gap nature of the superconducting state and indicates larger intraband diffusivity in the three-dimensional (3D) π band compared to that in the two-dimensional (2D) σ band. Direct comparison of our results with those reported previously for single crystals indicates that larger intraband scattering in the 3D π band leads to an increase of λ. We calculated λ and the thermodynamic critical field Hc ≈2000 Oe employing the gap equations for two-band superconductors. Good agreement between the measured and calculated λ value indicates the two independent measurements, such as magnetic force microscopy and transport, provide a venue for investigating superconducting properties in multi-band superconductors.

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“…In the following I will refer to the paper of A.F.Goncharov [5] because in there are present both measurement of the variation of critical temperature and of phonon mode by means of Raman measurement, with the pressure and so I mainly refer to these experimental data. In fact only in this work there are all input parameters necessary to my model.Let us start from the generalization of the Eliashberg theory [7,8] for systems with two bands [9], that has already been used with success to study the MgB 2 and related systems [10,11,12,13,14,15]. To obtain the gaps and the critical temperature within the s-wave, two-band Eliashberg model one has to solve four coupled integral equations for the gaps ∆ i (iω n ) and the renormalization functions Z i (iω n ):…”

mentioning

confidence: 99%

“…with [10,11] λ σσ (0) = 1.017, λ ππ (0)=0.448, λ σπ (0)=0.213 and λ πσ (0)=0.155. At the end, in this approximate model of electron-phonon coupling constants only λ σσ and λ πσ change with the pressure.…”

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confidence: 99%

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Pressure dependence of critical temperature in MgB2 and two-bands Eliashberg theory

Ummarino¹

2005

Physica C: Superconductivity and its Applications

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The variation of the superconducting critical temperature Tc as a function of the pressure p in the magnesium diboride M gB2 has been studied in the framework of two-bands Eliashberg theory and traditional phonon coupling mechanism. I have solved the two-bands Eliashberg equations using first-principle calculations or simple assumptions for the variation, with the pressure, of the relevant physical quantities. I have found that the experimental Tc versus p curve can be fitted very well and information can be obtained on the dependence of the electron-phonon interaction matrix < I 2 > by pressure. The pressure dependence of the superconductive gaps ∆σ and ∆π is also predicted.PACS numbers: 74.62.Fj; 74.20.Fg; 74.70.Ad, 74.25.Kc In the last few years, there is an noticeable increase of the study of superconductivity in many elements under pressure [1], such as sulphur (T c = 17 K), oxygen (T c = 0.5 K), carbon in nanotube (T c = 15 K) and diamond forms (T c = 4) K, a non-magnetic state of iron (T c = 1 K), and the light elements lithium (T c = 20 K) and boron (T c = 11 K). The application of external pressure to superconductors can drive the compounds towards or away from lattice instabilities by varying the principal parameters determining the superconducting properties (the electronic density of states at the Fermi energy, the characteristic phonon frequency, and the electron-phonon coupling constant), and it can be used to tune the T c and the superconducting properties. Almost all of the superconducting metallic materials, unlike the previous simple elements, show a decrease of T c with pressure. This negative pressure coefficient was attributed to the volume dependence of the electronic density of states at the Fermi energy and of the effective interaction between the electrons mediated by the electronphonon coupling. Measurements of the influence of pressure on the transition temperature and critical field yield information on the interaction causing the superconductivity. Indeed, the pressure would seem to be a variables whose effects might be capable of immediate theoretical interpretation. The binary alloy M gB 2 , superconductor [2], at ambient pressure, at T = 40 K has, under pressure, a behaviour similar to metallic materials. The magnesium diboride has stimulated intense investigation, both from the theoretical and the experimental point of view. Now the electronic structure of M gB 2 is well understood and the Fermi surface consists of two three-dimensional sheets, from the π bonding and antibonding bands, and two nearly cylindrical sheets from the two-dimensional σ bands [3]. There is a large difference in the electronphonon coupling on different Fermi surface sheets and this fact leads to a multiband description of superconductivity. Theory indicates that the strongest coupling is realized for the near-zone center in-plane optical phonon * Electronic address: E-mail:giovanni.ummarino@infm.polito.it (E 2g symmetry) related to vibration of the B atoms [1]. The superconductivity in M gB 2 has been ...

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Specific heat of MgB₂in a one- and a two-band model from first-principles calculations

Cited by 301 publications

References 35 publications

Theory of the critical current in two-band superconductors with application toMgB2

Theory of the critical current in two-band superconductors with application toMgB2

Measurement of the magnetic penetration depth of a superconducting MgB2thin film with a large intraband diffusivity

Pressure dependence of critical temperature in MgB2 and two-bands Eliashberg theory

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Specific heat of MgB2in a one- and a two-band model from first-principles calculations

Cited by 301 publications

References 35 publications

Theory of the critical current in two-band superconductors with application toMgB2

Theory of the critical current in two-band superconductors with application toMgB2

Measurement of the magnetic penetration depth of a superconducting MgB2thin film with a large intraband diffusivity

Pressure dependence of critical temperature in MgB2 and two-bands Eliashberg theory

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Specific heat of MgB₂in a one- and a two-band model from first-principles calculations